1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, a plotter, or a multi-functional system including a combination thereof.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member such as a photoconductor; an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
In such image forming apparatuses, after the toner image is transferred onto the recording medium, toner residue remaining on the surface of the image bearing member is removed by a cleaner such as a cleaning blade in preparation for the subsequent imaging cycle.
In a color-image forming apparatus, such as a tandem-type image forming apparatus, a plurality of photoconductors, one for each of the colors black, yellow, magenta, and cyan, are arranged in tandem facing a belt-type intermediate transfer member (hereinafter simply referred to as an intermediate transfer belt), and multiple toner images of a respective single color are formed on the photoconductive drums. Then, the toner images are transferred onto the intermediate transfer belt so that they are superimposed one atop the other, thereby forming a composite toner image. This process is known as a “primary transfer process”. After the primary transfer process, the composite toner image may be transferred onto a recording medium, in a process known as a “secondary transfer process”. Alternatively, the toner images may be directly transferred onto a recording medium carried on a sheet conveyance belt.
Some common problems with such an electrophotographic image forming apparatus are known. For example, poor cleaning of the photoconductive drums causes streaks in an output image, and electrical discharge in the transfer device causes voids.
When the cleaner employs a blade-type cleaning member, the blade tends to stiffen in a low-temperature, low-humidity environment. A cleaning blade that has stiffened cannot conform to the surface of the photoconductor, preventing the cleaning blade from contacting the photoconductor evenly.
To address this difficulty, a heater such as a wire heater may be disposed near the photoconductor. However, as is generally the case, because various imaging devices are disposed around the photoconductor there is no extra space near the photoconductor for disposing the heater near the photoconductor. Consequently, the heater is typically located some distance from the photoconductor. In this case, however, the temperature near the photoconductive drums varies from locally, causing variation in the performance of the cleaner but also affecting the electrical resistance of the transfer member. That is, electrical resistance in general varies with temperature and humidity, and is high in a low-temperature, low-humidity environment and low in a high-temperature, high-humidity environment. As the electrical resistance of the transfer member increases, electrical discharge occurs in the transfer device, causing voids in the output image.
Thus, for example, in wintertime, if the image forming apparatus is turned on in the morning, the electrical resistance of the transfer member is too high, generating an electrical discharge. As a result, during the transfer process, the electrical discharge causes a void in the toner image. To a certain extent this problem is self correcting: As the image forming apparatus remains in operation continuously, the internal temperature of the image forming apparatus rises, thereby decreasing the electrical resistance of the transfer member. Accordingly, an image with voids is not produced. But the problem of consistency remains unresolved.
In view of the above, there is demand for an image forming apparatus that is capable of reliably producing good images regardless of temperature variance.